A library apparatus has a plurality of cells each for storing a cartridge such as a magnetic tape cartridge or an optical disk cartridge in which an information recording medium is contained. The cartridge stored in any cell selected from the plural cells is loaded into a drive unit provided in the library apparatus. Then, information processing is carried out on the medium contained in the loaded cartridge by the drive unit. More specifically, information recording and/or reproduction is carried out on the medium by the drive unit.
The library apparatus usually has a cartridge access station (CAS) for allowing insertion and ejection of the cartridge. The library apparatus further has an accessor robot acting on the cartridge to transfer the cartridge among the cartridge accessor station, each cell, and the drive unit.
In a large-scale library apparatus, the accessor robot is moved along at least one straight line in the horizontal direction, to enable efficient transfer of the cartridge.
For example, in a library apparatus described in Japanese Patent Laid-open No. 8235729, an accessor robot is moved by a drive force of its own motor along a straight rail extending in a horizontal direction.
To supply electric power to the accessor robot or transfer a control signal, a flat cable is connected to the accessor robot. In a large-scale library apparatus, the accessor robot moves over 20 m in some cases, and accordingly the flat cable tends to become long, so the apparatus must handle such a long flat cable well.
To apply a given tension to the flat cable and thereby prevent slack of the flat cable irrespective of a moving position of the accessor robot, a wire rope and an idler pulley (running pulley) may be used, for example. One end of the wire rope is connected to a housing of the library apparatus, and the other end of the wire rope is connected to the accessor robot. When the accessor robot moves a certain distance, the idler pulley moves half the distance. Accordingly, by wrapping the flat cable around a cable drum moving with the idler pulley, fixing one end of the flat cable to the accessor robot, and fixing the other end of the flat cable to the housing, a constant tension is always applied to the flat cable.
In the case of supplying electric power to the accessor robot or transferring a control signal by using the flat cable connected to the accessor robot, at least part of the flat cable is moved with the accessor robot, so that mechanical damage to the flat cable is expected. For example, when a feeder mechanism including the idler pulley and the cable drum mentioned above is adopted, the flat cable may be worn or damaged by the friction between it and the cable drum.
In the event that damage to the flat cable progresses, a signal line pattern included in the flat cable may be broken, disrupting normal operation of the accessor robot.
It may be proposed that a check line formed of a conductor is provided in the flat cable independently of the signal line pattern, and a current is passed through the check line to detect a break in the check line according to the current, thereby electrically detecting damage to the flat cable. Accordingly, the accessor robot can be stopped immediately when a break in the check line is detected.
However, in a system configured so that the accessor robot is stopped suddenly upon detection of a break in the check line, the emergency stop of the accessor robot cannot be predicted. Accordingly, the accessor robot becomes suddenly inoperable, resulting in unavoidable stall or failure of the system, including the library apparatus.
The damage to the flat cable is considered to proceed gradually as the cable wears, so if the damage to the flat cable can be detected early, any protection such as replacement of the flat cable may be possible without unexpectedly stopping the accessor robot. Thus, early detection of the damage to the flat cable is considered very useful for prevention of system failure.